Visiting my partner's family hometown in Fukuyama we stumbled on Koyama Motors (小山自動車) - which turned out to be a local shop run by two brothers for over 50 years with amazing history - they are reknown in the area for servicing and repairing any make or model - and when we visited they were rebuilding a Ferrari engine, while also working on a R33 Skyline, AE86, a Porsche and an older Mercedes.
With the help of my partners mum translating we were able to chat with them a little and once they worked out that I was interested in what they were doing and knew a bit about cars they showed me a magazine article of a Gymkhana S13 they built in collaboration with Nismo in the 80's. There was an hour long documentary on the shop from a Japanese television station that they also showed me - linked HERE. Their reputation in the region made sense when they showed me around as they had every piece of machinery imaginable and every manual you could think of across so many different models, and they explained that everything is done in house, from servicing to engine machining and complete rebuilds.